FIG. 4 is a perspective view showing a modular encoder 1 according to the prior art. The modular encoder 1 comprises a fixed member 2 to be fixed to a rotary shaft of a motor, and a cage 3 attached to a motor body. The fixed member 2 includes a hollow and cylindrical boss 4 fitted in a rotary shaft, and a transparent/shading member, that is, a pulse disk 6 which has a transparent region and a shading region formed thereon and is fixed to the boss 4 with a clamp 5. The cage 3 includes an electric substrate 8 on which an optical sensor is provided, and a locking member 9 on which a light source is provided. The cage 3 is secured, with a screw 10, to the locking member 9 attached to the motor body. The modular encoder 1 according to the prior art is a separate type modular encoder capable of separating the fixed member 2 from the cage 3 having the electric substrate 8 in a detector.
The boss 4 is fitted in the rotary shaft of the motor and the fixed member 2 is fixed to the rotary shaft with a set vis 11 from the side. Light transmitted from the light source is irradiated on the pulse disk 6, an optical sensor receives, as a light signal, the light which has passed through the transparent region of the pulse disk 6 and converts the light signal into an electric signal, and electric parts provided on the electric substrate 8 output the electric signal as a rotational position signal of the motor. The electric substrate 8 and the locking member 9 according to the prior art have circular shapes as shown in FIG. 4, respectively.
In the modular encoder 1 according to the prior art, however, the set vis 11 should be fastened with a screw from the side perpendicularly to the rotary shaft when fixing the fixed member 2 to the rotary shaft. Therefore, the fixed member 2 is fixed only in a certain direction of the rotary shaft. Accordingly, it has been necessary to take measures for preventing small looseness of the set vis from being caused by restriction of assembly and dimensions.
Since the electric substrate 8 and the locking member 9 have circular shapes, it is hard to reduce the size of the modular encoder 1. More specifically, also in the case where only a dimension in a particular direction should be reduced, the size of the whole body has to be reduced.
Furthermore, the pulse disk 6 is uncovered. For this reason, there has been a possibility that fingers might be injured by the pulse disk 6 when performing assembly or adjustment which needs delicate sensation of the tips of the fingers. In particular, in the case where the pulse disk 6 is formed of a thin metal plate, workers should surely take care.
It is an object of the present invention to provide a modular encoder which has a small size, can easily be assembled, has high reliability, has excellent fixing properties, can be manufactured at a low cost, and has excellent environment resistance.